Pickup tube assembly



Sept. 1960 L. D. MILLER ET AL PICKUP TUBE ASSEMBLY Filed May 22, 1959 K E mnn wEM VLY mmD R DE U U ME armawiy PICKUP TUBE ASSEMBLY Filed May 22, 1959, Ser. No. 815,193

2 Claims. 01. 31s s9 This invention relates to pickup tubes. In particular, this invention relates to an improved mesh support and particle barrier sub-assembly for a photoconductive type pickup tube.

In the prior art, certain photoconductive type pickup tubes are well known. One of the conventional tubes of this type is a pickup tube known as a Vidicon. In the Vidicon type pickup tube, a photoconductor is positioned on a transparent conducting signal plate and is exposed to light from a scene to be reproduced. Spaced from the free side of the photoconductor is a fine mesh screen through which the photoconductor is scanned by an electron beam. The photoconductor changes its conductivity in response to the light from the scene, so that a charge pattern is. developed on the beam side of the photoconductor in proportion to the light and shade of the scene. When the electron beam scans the photoconductor, the charge pattern is discharged and output signals are produced on the signal plate.

One of the problems relating to tubes of this type, and which has made these tubes difiicult to manufacture, is that dust and dirt particles may be deposited on the p'hotoconductor or may contaminate the fine mesh screen. These dust particles, at times, come from memberswithin the envelope, and at other times from the surrounding atmosphere during the manufacturing stages of States Patent the tube. These dust particles may be deposited in these areas during the manufacturing steps, or during the operation of a completed tube when the tube is focused in a downward direction. 7 Another problem in manufacturing pickup tubes of this type is that their complicated structure interferes with a desired quick and inexpensive assembly of such tubes.

It is, therefore, an object of this invention to provide a new and improved pickup tube and a novel method of manufacturing the same.

It is another object of this invention to provide a novel mesh support and particle barrier for a pickup tube.

These and other objects are accomplished in accordance with the invention by providing a mesh support, which is press-fitted into the tube as one of the latter steps of assembling the tube, and which clamps a particle barrier into a position that extends from a region adjacent to the final accelerating electrode to the envelope wall.

The invention will be more clearly understood by referring to the accompanying single sheet of drawing wherein:

Fig. 1 is a longitudinal sectional view of a pick-up tube in accordance with this invention; and

Fig.2 is an enlarged fragmentary sectional view of the tube shown in Fig. 1.

Reference specifically to Fig. 1 will reveal a photoconductive pick-up tube 10 comprising an evacuated envelope 11 having an electron gun 12 in one end thereof. The envelope 11 is preferably a precision bulb, i.e. one

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2. that is held in fairly close tolerances with respect to rou-ndness, thickness and diameter. The electron gun 12 is conventional and is supported within the end of envelope 11 by means including a plurality of lead-in wires 14. The electron gun produces an electron beam which is accelerated and focused by a plurality of electrodes 16, 18 and 20 toward a target electrode 22.

The target electrode 22 comprises a transparent signal plate 24 that is supported upon a transparent face plate 2-6. Covering the transparent signal plate 24 is a layer of photoconductive material 28. The target electrode 22 may be made of conventional materials, examples of which are glass for the face plate 26, tin oxide for the transparent signal plate 2-4, and antimony tri-sulphide for the photoconductor 28.

The face plate 24 is sealed to the open end of the envelope 11 by means of a ring of indium 30 which is retained within a ring of harder metal 32. A more thorough description of the indium seal, and the process for making the same, may be found in a copending application of B. H. Vine, Serial No. 648,094, filed March 25, 1957, and assigned to the assignee of this invention. The important feature of the seal, as related to this invention, is that the seal is made after the electrodes 12, 16, 18 and 20 have been mounted within the envelope, and after the transparent conductor 24 and photoconductor 28 have been deposited on the transparent face plate 26. In other words, the forming of the face plate seal is one of the later steps of assembling the tube.

Reference now to Figs. 1 and 2 for a description of this invention will reveal a tube structure including 'a bulb spacer 34. The bulb spacer 34 contacts the inner surface of the envelope 11 and extends over the end of the electrode 20. The bulb spacer 34 is spot welded onto the inner surface of the electrode 20 adjacent the upper end thereof, as viewed in Figs. 1 and 2. It should be noted that the bulb spacer 34 maintains the upper end of the electrode 20 centrally located within the envelope 11. Press-fitted into the bulb spacer 34 is a mesh mounting ring '36 which has a flanged end 36' that extends into the bulb spacer 34. It should be noted that the flanged end 34 of the bulb spacer 34 contains slots 37 which permit the compression of the end 36' to press-fit into the bulb spacer. Bonded between the mesh support ring 36 and a ring 40 is a fine mesh screen 42. The mesh screen 42 is preferably, of the electroformed type having 500 to 1000 apertures per inch. The mesh screen 42 is bonded between the mesh support ring 36 and the ring 40 by conventional methods, such as spot welding the two rings together while the mesh is positioned therebetween. The ring 40 may be omitted if desired, although for simplicity of manufacture, it has been found easier to support the mesh by bonding rings 36 and 40 together while the mesh screen is between the rings.

Sandwiched between the ring 36 and the portion of the bulb spacer 34 that extends over the upper end of the electrode 20 is a particle barrier 44. The particle barrier 44 is in the form of a thin ring having a very accurately controlled outside diameter. It should be noted that the particle barrier is larger than the space between the electrode 20 and the inner diameter of the envelope 11 and, when positioned, is bent toward the target 22. The particle barrier 44 is held in position between the ring 36 and the bulb spacer 34, by pressfit-ting the flange portion 36' into the bulb spacer 34. The particle barrier is thus not fixedly attached to either the bulb spacer on the ring, and is clamped iii position solely by a friction fit. As a result of this ar- 3 rangement, the particle barrier makes positive contact with the bulb wall.

A nickel chromium alloy may be used as the metal for forming the elements. Thicknesses of the particular elements which have been found satisfactory are as follows:

Thickness, Inside diam- Outside Element inches eter, inches Diameter,

7 inches Bulb Spacer 34 0055 739+. 002 1. 000+. Support ring 36 .015 .704 870+: 005

Ring 40 (J 750+. 005 .870+. 005 Particle Barrier 44 Q .005 .786]-. 005 .926+.

It should be understood that the above sizes and materials are given merely as an example of a successful embodiment of the invention, and the invention should not be limited to these particular dimensions or materials.

The tube 10 is assembled as follows, in accordance with this invention: After the electrodes 12, 16, 18 and Ztl, and the bulb spacer 34, have been mounted within the envelope, and after the target 22 has been deposited on the face plate 26, the sub-assembly including the support ring 36, the ring 40 and the particle barrier 44 are snapped in by press-fitting, or friction-fitting the flanged portion 36' into the bulb spacer 34. Since this press-fitting occurs from the target end of the envelope 11, the particle trap 44 will scrape or wipe the envelope .11 and remove dust particles from the target area and force these dust particles back toward the electron gun where they are relatively harmless. Also, it should be noted that the particle barrier has the advantage of isolating the weld splashes of the bulb spacer and electrode 20 from the photo-cathode or target.

After the mesh assembly and bulb spacer have been press-fitted into the electrode 26, the face plate 26 and its target 22 are sealed to the end of the envelope by pressure on the indium ring 30, as is described in the above identified copending application. This seal should be made as soon after the insertion of the mesh assemblyparticle trap as possible, so that mesh electrode 43 and the walls of the envelope 11 between the particle trap 44 and the target 22 will remain as clean as possible.

A snap-in assembly, in accordance with this invention, is easily manufactured and provides a particle barrier that not only functions as a barrier but, by means of its insertion, functions to remove dirt particles from the critical area of the tube. Also, when practicing this invention, the mesh may be inserted in one of the final manufacturing steps, which decreases the possibility of the mesh becoming contaminated during the manufacture of the tube. Thus, the combination of the new meshparticle banier insertion method, and the improved particle barrier, will make cleaner tubes initially, and will keep the tubes clean when the tubes are operated in any position.

What is claimed is:

1. A sub-assembly for a pickup tube comprising a hollow tubular envelope, a hollow tubular electrode within said envelope and spaced from the walls of said envelope, a bulb spacer having a plurality of finger-like members contacting the inner surface of said envelope,

said spacer further including a solid portion extending over an end of said hollow tubular electrode and bonded to the inner surface of said electrode, a particle barrier extending from a region adjacent to said tubular electrode and to said inner surface of said envelope, a mesh screen, a hollow tubular mesh screen support ring having a flanged portion bonded to said mesh screen, and a friction fit between the outer surface of the tubular por tion of said support ring and the inner surface of said solid portion of said spacer, said particle barrier being clamped between said support ring and said spacer.

2. A sub-assembly for a pickup tube comprising an elongated envelope, a transparent face plate sealed across an end of said envelope by means of an indium ring, said sub-assembly comprising a hollow tubular electrode within said envelope, an end of said electrode being spaced from and closely adjacent to said face plate, a' bulb spacer extending from the interior of said electrode and over said end and away from said face plate and into contact with the inner wall of said envelope, a mesh support ring having a mesh bonded thereacross, a tubular mesh support member having a portion thereof bonded to said support ring, another portion of said support member being friction-fitted into the portion of said bulb spacer within said electrode, and a particle barrier extending from said portion of said bulb spacer extending over the end of said electrode and to said inner wall of said envelope and toward said indium ring, said particle barrier being clamped between the portion of said support member bonded to said ring and said portion of said bulb spacer extending over said end of said electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,514,878 Kuperus July 11, 1950 2,544,753 Graham Mar. 13, 1951 FOREIGN PATENTS 1,141,316 France Mar. 11, 1957 

